It is known to use light level measurement instruments to measure attenuation in fiber optic cables. Such instruments are useful in testing for breaks in continuity or other defects causing excess attenuation in the cable. Typically, such instruments use a high-power LED emitter to transmit light into one end of the cable. The other end of the cable is connected to a light level detector, such as a photodiode. A comparison of the light level received by the detector, relative to the light input by the LED, indicates the attenuation across the cable. Cables having defects causing excess attenuation are discovered when the measured attenuation exceeds the levels known to exist in defect-free cables of the same length.
This invention is related to an adaptable connector for connecting fiber optic cables to such a test set.
Fiber optic cables are provided with terminal connectors prior to their inclusion in an optical circuit. The terminal connectors are used to hold the small diameter glass fiber of the cable in optical alignment with other fibers, light sources, or light receivers. There are a wide variety of such connectors in current use. This variety creates a problem for fiber optic test instruments (hereinafter referred to as test sets) of the type described above. In the test set, the optical fiber must be held in precise coaxial alignment with the LED and, to a lesser extent, with the detector. With the wide variety of terminal connectors in use, the plug-in terminals of a test set may only be compatible with one type of connector.
One commercial test set provides interchangeable plug-in modules that make it possible to adapt the set to accommodate a variety of connectors. However, the module must be changed for each type connector. Another solution, when testing a cable before a terminal connector has been applied, is to attach a terminal connector that is compatible with the test set, and then later remove the connector and replace it with another connector to be used in a circuit.
In view of the above problems associated with testing fiber optic cables, it is an object of the present invention to provide an adaptable connector in a test set whereby fiber optic cables may be tested without permanent terminal connectors. It is necessary for such connector to provide precise alignment and support for the thin optical fiber, and to hold the fiber in precise coaxial alignment with the LED and light detectors. Moreover, it is particularly desirable that the adaptor be able to accommodate cables having differing diameters and having optical fibers of differing diameters. The present invention provides both of these desirable features.